If the Bird is smart, you can't beat him.
Point is if any race is smart you can't beat them. There is always a way, all you have to do is read donovan really carefully.
He stayes cloaked... so what? You stay cloaked as well. And lay mines.
He attacks your bases? Protect them with a strong ship you got from another races. If he tries to tow it away, you have a Lady and force surrender.

The best way would of course be to convince him to ally with you. Bird+ priv is a really deadly alliance, because you can avoid Lokis and Iron storms while he can benefit from the meteors and the things you capture. evil.

OK, sometime you just loose. But you can still make him pay, especially as privateer.
Don't give up, just be patient.